1. Field of the Invention
The present invention relates to an image recording apparatus for recording an image onto a thermal recording material including a transparent support and a plurality of transparent thermal color-developing layers which are respectively developed in different hues and are provided on both sides of the transparent support. 2. Description of the Prior Art
At present, there is known a thermal recording method for recording an image onto a recording paper by the use of a heating element. In this thermal recording method, a thermal recording material is used which is coated with a color-developing agent and a developer on a support such as paper, synthetic paper or the like. An image is recorded onto the thermal recording material by a thermal head on the basis of a process in which the thermal recording material is heat-processed. Such a thermal recording method has the following advantages, i) development is unnecessary, ii) in case where the support is paper, the paper quality is approximates that of generally used paper, iii) handling is easy, iv) the density of color development is high, v) The recording device is simple and of low cost, and vi) noise at the time of recording is less than that of a dot printer or the like. Thus, this thermal recording method has rapidly spread in recent years in the field of black-and-white facsimiles and printers.
Further, accompanying the rapid expansion and developments in the information industry, the demand for color hard copies from general terminal equipment, including computers and facsimiles has increased. In order to obtain multi-color thermal recording material, however, it is required that color-developing mechanisms corresponding in number to the developed colors be incorporated on the same support, and be controllable. In spite of the fact that a great deal of effort has been made, the hues of color development and color separation have not been satisfactory.
An opaque support such as paper, synthetic paper or the like is normally used as a support for the thermal recording material. This is merely due to the fact that a color-developing image is read as a reflective image from one side of the support.
Further, examples in which a transparent support is used as a support for thermal recording material, are disclosed in Japanese Patent Publication No. SHO 40-20151 and Japanese Patent Application Laid-Open Nos. SHO 61-227086 and SHO 62-44492, whose purposes are such that a thermally recorded recording image is viewed from one side of the transparent support to thereby obtain a high-contrast image or a high-quality image superior in luster or gloss. Further, it has also been proposed in Japanese Patent Application Laid-Open Nos. SHO 49-114431, SHO 50-3640 and SHO 60-4092 that thermal recording layers different in color-developing hue from each other are provided on both sides of the transparent support member, to obtain a color image having two colors or a plurality of colors.
However, in these cases each of the thermal color-developing layers includes color-developing components and developer components merely dispersed in a solid condition. Accordingly, the thermal color-developing layer per se is made substantially opaque due to diffuision of light. Thus, it is impossible to obtain a clearly color-divided multi-color image. In the invention disclosed in the aforesaid Japanese Patent Application Laid-Open No. SHO 60-4092, in order to improve transparency of the thermal color-developing layer, various components are dissolved and are coated onto the same layer. In this case, however, since color development in the various components is easily caused to occur before printing, a so-called fog or blushing occurs. Accordingly, the possible or potential numbers of color division are lowered and the material disclosed in the above Japanese provisional publication is essentially insufficient as a multi-color recording material.
In Japanese Patent Application Laid-Open Nos. SHO 63-45084 and SHO 63-252783, the applicant has proposed that color-developing layers, which are substantially transparent and are developed in color to hues different from each other, are provided on both sides of a transparent support, whereby it is possible to obtain a thermal color-developing image which is superior to the conventional one.
According to the proposal, it is possible to obtain a multi-color image which is superior in hue, superior in color separation, and superior in image reservation, than is conventionally obtained by the thermal recording system. Further, the obtained image can be image transparent image, reflective.
Since such thermal recording paper is provided at both sides with color-developing layers, it is required that both sides be heated respectively by thermal heads. Further, in the case were a plurality of color-developing layers are provided on one side of the thermal recording material, it is required that the uppermost layer, that is, a layer most proximate to the surface of the support, be heat-developed by a heat quantity of an order such that the other layers are not heated, and the color-developing layer is then fixed before heat-processing the other color-developing layers. A principal or basic image recording process or procedure will be described hereunder with reference to FIG. 4 of the accompanying drawings.
As shown in FIG. 4(A), a thermal recording material 10 comprises a polyester film (hereinafter referred to as "PET") 102 which serves as a support for the thermal recording material 10. A magenta-pigment layer (hereinafter referred to as "M-pigment layer") 104 is provided on one side of the PET 102. An yellow-pigment layer (hereinafter referred to as "Y-pigment layer") 106 is provided on the M-pigment layer 104. A cyan-pigment layer (hereinafter referred to as "C-pigment layer" 108 is provided on the other side of the support. All of these components are transparent. In this connection, the Y-pigment layer 106 is a light fixing type, and has such a nature that light of a wavelength of 400 nm, when applied to the Y-pigment layer 106 from a light source 109, will fix the layer whereby no change subsequently occurs in the Y-pigment layer 106 even if the latter is heated. In case of a thermal recording material, in which a white layer (not shown) is provided on the Y-pigment layer 106, the image can be viewed as a reflective image from the side of the C-pigment layer 108. A recording head 110 is arranged above the thermal recording material 10.
First, in FIG. 4(A), the Y-pigment layer 106 is heat-processed by the thermal head 110. In this case, the heat quantity applied to the M-pigment layer 104 beneath the Y-pigment layer 106 is such that the M-pigment layer 104 is not developed in color by the heat quantity. By doing so, only the Y-pigment layer 106 is developed in color.
Subsequently, in FIG. 4(B), light whose wavelength is of the order of 400 nm, is applied from the side of the Y-pigment layer 106. Thus, the Y-pigment layer 106 is fixed, and no change in color occurs at subsequent heating.
In FIG. 4(C), the M-pigment layer 104 is heat-processed by a heat quantity that is larger than that at the time the Y-pigment layer 106 is heated. By doing so, the M-pigment layer 104 is developed in color.
Subsequently, in FIG. 4(D), the thermal recording material 10 is reversed. In FIG. 4(E), the C-pigment layer 108 is heated-processed. Further, in the case where another recording head 112 as indicated by the double dotted lines in FIG. 4(A) is arranged beneath the thermal recording material 10, the C-pigment layer 108 is heat-processed under a condition that the C-pigment layer 108 remains intact. In this case, the C-pigment layer 108 is heated by such a heat quantity that no influence is exerted on the M-pigment layer 104 which cooperates with the C-pigment layer 108 to clamp therebetween the PET 102. Thus, the C-pigment layer 108 is developed in color.
However, a condition for obtaining an image recording apparatus which records an image onto multi-color thermal recording material is that, since the same image is recorded divided into three steps to reproduce the color of the image, it is necessary that the thermal recording material is accurately positioned. As far as accurate positioning cannot be automatically processed, it becomes difficult to process the multi-color thermal recording material at high speed as in the conventional image recording apparatus. Further, as shown in FIG. 4(A), if the recording heads 110 and 112 are arranged respectively on the both sides of the thermal recording material 10, the reversing operation of the thermal recording material 10 as shown in FIG. 4(D) is dispensed with. However, The number of component parts increases, and the apparatus per se also increases in size. Thus, this is not preferable.